The functional role of the eukaryote-specific motif YxxPKxYxK of the human ribosomal protein eS26 in translation

Functional involvement of a conserved motif in the middle region of the human ribosomal protein eL42 in translation

Ribosomal protein eL42 (formerly known as L36A), a small protein of the large (60S) subunit of the eukaryotic ribosome, is a component of its exit (E) site. The residue K53 of this protein resides within the motif QSGYGGQTK mainly conserved in eukaryotes, and it is located in the immediate vicinity of the CCA-terminus of the ribosome-bound tRNA in the hybrid P/E state. To examine the role of this eL42 motif in translation, we obtained HEK293T cells producing the wild-type FLAG-tagged protein or its mutant forms with either single substitutions of conserved amino acid residues in the above motif, or simultaneous replacements in positions 45 and 51 or 45 and 53. Examination of the level of exogenous eL42 in fractions of polysome profiles from the target protein-producing cells by the Western blotting revealed that neither single substitution affects the assembly of 60S ribosomal subunits and 80S ribosomes or critically decreases the level of polysomes, but the latter was observed with the double replacements. Analysis of tRNAs bound to 80S ribosomes containing eL42 with double substitutions and examination their peptidyl transferase activity enabled estimation the stage of the elongation cycle, in which amino acid residues of the conserved eL42 motif are involved. We clearly show that cooperative interactions implicating the eL42 residues Q45, Q51, and K53 play a critical role in the ability of the human ribosome to perform properly elongation cycle at the step of deacylated tRNA dissociation from the E site in the human cell.

Two "Edges" in Our Knowledge on the Functions of Ribosomal Proteins: The Revealed Contributions of Their Regions to Translation Mechanisms and the Issues of Their Extracellular Transport by Exosomes

Ribosomal proteins (RPs), the constituents of the ribosome, belong to the most abundant proteins in the cell. A highly coordinated network of interactions implicating RPs and ribosomal RNAs (rRNAs) forms the functionally competent structure of the ribosome, enabling it to perform translation, the synthesis of polypeptide chain on the messenger RNA (mRNA) template. Several RPs contact ribosomal ligands, namely, those with transfer RNAs (tRNAs), mRNA or translation factors in the course of translation, and the contribution of a number of these particular contacts to the translation process has recently been established. Many ribosomal proteins also have various extra-ribosomal functions unrelated to translation. The least-understood and -discussed functions of RPs are those related to their participation in the intercellular communication via extracellular vesicles including exosomes, etc., which often carry RPs as passengers. Recently reported data show that such a kind of communication can reprogram a receptor cell and change its phenotype, which is associated with cancer progression and metastasis. Here, we review the state-of-art ideas on the implications of specific amino acid residues of RPs in the particular stages of the translation process in higher eukaryotes and currently available data on the transport of RPs by extracellular vesicles and its biological effects.

Ribosomes: The New Role of Ribosomal Proteins as Natural Antimicrobials

Moonlighting proteins are those capable of performing more than one biochemical or biophysical function within the same polypeptide chain. They have been a recent focus of research due to their potential applications in the health, pharmacological, and nutritional sciences. Among them, some ribosomal proteins involved in assembly and protein translation have also shown other functionalities, including inhibiting infectious bacteria, viruses, parasites, fungi, and tumor cells. Therefore, they may be considered antimicrobial peptides (AMPs). However, information regarding the mechanism of action of ribosomal proteins as AMPs is not yet fully understood. Researchers have suggested that the antimicrobial activity of ribosomal proteins may be associated with an increase in intracellular reactive oxidative species (ROS) in target cells, which, in turn, could affect membrane integrity and cause their inactivation and death. Moreover, the global overuse of antibiotics has resulted in an increase in pathogenic bacteria resistant to common antibiotics. Therefore, AMPs such as ribosomal proteins may have potential applications in the pharmaceutical and food industries in the place of antibiotics. This article provides an overview of the potential roles of ribosomes and AMP ribosomal proteins in conjunction with their potential applications.